Mercury methylation upon coastal sediment resuspension: a worst-case approach under dark conditions

• Published in: Environmental monitoring and assessment Vol. 194; no. 11; p. 805
• Main Authors: Monte, Christiane N., Rodrigues, Ana Paula C., Galvão, Petrus M. A., Pontes, Gabriela C., Malm, Olaf, Wasserman, Júlio C., Machado, Wilson
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01.11.2022; Springer Nature B.V
• Subjects: Atmospheric Protection/Air Quality Control/Air Pollution; Bay water; Bottom trawling; Coastal sediments; Correlation; Demethylation; Dimethylmercury; Dredging; Earth and Environmental Science; Ecology; Ecotoxicology; Environment; Environmental Management; Environmental monitoring; Environmental science; Estuaries; Estuarine dynamics; Evaluation; Fluvial sediments; Harbors; Mercury; Mercury (metal); Methyl mercury; Methylation; Methylmercury; Monitoring/Environmental Analysis; Photolysis; Resuspension; Rivers; Sediment; Sediments; Statistical analysis; Temporal variability; Temporal variations; Toxicity; Brazil; Rio de Janeiro Brazil; Estuaries; Dredging activities; Bioavailability; Harbor; Chlor-alkali plant
• ISSN: 0167-6369; 1573-2959
• DOI: 10.1007/s10661-022-10485-y

Mercury behavior upon resuspension of sediments from two impacted areas of Guanabara Bay was evaluated to assess worst-case methylmercury (MeHg) responses, under dark experimental conditions to prevent demethylation by photolysis. Study areas include the Rio de Janeiro Harbor (RJH) and the chlor-alkali plant–affected Meriti River (MR) estuary. Total mercury (THg) and MeHg concentrations were determined along 24-h experiments of sediment resuspension in the bay water in dark conditions. Fine-grained Meriti River (MR) estuary sediments had 8 times higher MeHg initial concentrations than sandy Rio de Janeiro Harbor (RJH) sediments (3.4 ± 0.29 vs. 0.41 ± 0.1 ng g −1 , respectively). Though THg contents were uncorrelated with resuspension time, statistically significant correlations of MeHg ( r s  = 0.78) and %MeHg in relation to THg ( r s  = 0.86) with resuspension time were observed for RJH sediments, indicating net methylation only for this study site. These positive correlation trends correspond to a 2.8 times MeHg concentration increase (ΔMeHg = 0.75 ng g −1 ) and 4.4 times increase in %MeHg (Δ%MeHg = 1.0%), after 24 h of resuspension. This suggests that assessments of factors affecting the MeHg spatial–temporal variability and associated toxicity risks can be limited in some sites if concentration changes due to sediment resuspension-redeposition processes are not considered. Therefore, the inclusion of MeHg evaluation before and after sediment resuspension events is recommendable for the improvement of dredging licensing and monitoring activities.